Conventionally, electrospinning (electric charge induced spinning) is known as a method for producing nanofibers formed from a polymer material which have a diameter in the order of submicrons. In conventional electrospinning, a polymer solution is supplied to a needle-like nozzle to which a high voltage is applied so that the polymer solution discharged as filaments from this needle-like nozzle is electrically charged. As the solvent of the polymer solution evaporates, the distance between these electric charges decreases, and the Coulomb force acting thereon increases. When this Coulomb force exceeds the surface tension of the filamentous polymer solution, the filamentous polymer solution is explosively drawn. This phenomenon, which is called electrostatic explosion, repeats as primary, secondary, and sometimes tertiary explosions and so on. As a result, nanofibers formed from a polymer with a diameter in the order of submicrons are produced.
By depositing the thus-produced nanofibers on a substrate that is electrically grounded, a thin film having 3-D structure of a 3-D mesh can be obtained, and by forming this film more thickly, a highly porous web having a submicron mesh can be produced. The thus-produced highly porous web can be preferably used as a filter, a battery separator, a polymer electrolyte membrane or an electrode for a fuel cell or the like. Application of the highly porous web made of these nanofibers is expected to dramatically improve the performance of those devices.
However, in conventional electrospinning, only one to a few nanofibers can be produced from the tip of a single nozzle. Therefore, productivity when trying to produce a highly porous polymer web does not improve, and thus such a polymer web could not be realized. Consequently, for example, as a method for producing a polymer web by producing a large amount of nanofibers, a method using a plurality of nozzles has been proposed (see Patent Document 1).
The configuration of the polymer web production apparatus described in Patent Document 1 will now be described with reference to FIG. 21. A liquid polymer material in a barrel 83 is fed to a spinning unit 82 having a plurality of nozzles 81 by a pump 84. A high voltage of from 5 to 50 kV is applied to the nozzles 81 by a high-voltage generation unit 85. Fibers discharged from the nozzles 81 are deposited on a collector 86 that is either grounded or charged with a polarity different to that of the nozzles 81 to form a web. The formed web is transported by the collector 86, whereby the polymer web is produced. Patent Document 1 also describes that a charge distributor 87 is arranged near the tips of the nozzles 81 to minimize electrical interference among the nozzles 81, and that a high voltage is applied between the charge distributor 87 and the collector 86 so that an electric field which urges the charged fibers towards the collector 86 is created.
Furthermore, as illustrated in FIGS. 22A and 22B, Patent Document 1 also describes that instead of providing a plurality of single nozzles, a plurality of multi-nozzles 81A, each including a plurality of nozzles 81 so that a plurality of nanofibers is produced from each of the multi-nozzles 81A.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-201559